Many computer applications today demand high network bandwidth over the internet. Good examples are systems that download large amount of data such as files, music or videos. Most of the internet traffic today is carried out via the Transmission Control Protocol (TCP). The main advantage of TCP is that it provides reliable data transfer to the application layer. The application does not have to deal with lost data packets, corrupted data packets, or out-of-order arrival of packets. All types of error detection and retransmission algorithms are already implemented in the TCP protocol. Also, sophisticated methods for congestion avoidance and flow control have been added to the TCP protocol. Most of these methods are intended to optimize bandwidth, i.e., data throughput, over a network.
Maximized data throughput usually comes at the price of increased latency. For example, a common technique is to not send out small pieces of data immediately but to wait until more data is available, so that larger packets can be sent then (e.g. Nagle algorithm). This increases bandwidth but also introduces extra delay. Another approach is to send out large amounts of data before getting an acknowledgement by the receiver. This also increases bandwidth but at the same time may increase the time a data packet is in transfer.
For many applications maximum bandwidth is by far the most important criterion. Increased latency is often not a problem. This is not true for applications like voice over Internet Protocol (IP) or teleconferencing. Here low response times, i.e. low latency, are crucial. These applications usually disable the Nagle algorithm or do not use TCP at all. Often bandwidth requirements are not that high for such applications.
Another class of applications requires both high bandwidth and low latency. This is true for example for a client-server based medical image viewer. Such a system needs to display large amounts of image data which are streamed from the server to the client. Often it is advisable to send images before they are requested by the client such as in traditional streaming applications. For example, if a doctor looks at the first image of a 3D image series then it is likely that she will also look at the second image soon. But if the doctor proceeds, some images that are scheduled for later streaming suddenly have to be transferred immediately, or images have to be rendered on the server and then displayed on the client as soon as possible. Thus it is important that the server stays always responsive and that new data can be sent as quickly as possible to the client based on current user interaction.
A general aspect of network based applications is that often not all parameters of the network are known, or can be influenced by the application. For example routers or other network devices between the endpoints may introduce latencies and buffers that are not application controlled. Often the network has to be regarded a black box.